Radiating cone antenna

ABSTRACT

A radiating cone antenna having a conical reflecting surface and a parabolic reflecting surface in spacial relationship and surrounding said conical reflecting surface. A linear directive radiator is positioned at the focus of the parabolic reflecting surface and energy from the radiator is reflected from the parabolic reflecting surface to the conical reflecting surface which, in turn, reflects the energy in a constant phase front.

7- l7-73 XR 397479116- Umted States Patent 1 91 111 3,747,116 Milam July 17, 1973 [54] RADIATING coNE ANTENNA 3,345,398 1611936 Massey etal. 343/838 22,676 21965 Hogg 343/837 [76] 4000 Mamsm 3,633,209 1/1972 Afifi ..343/840 Place, lndianapolls, 1nd. 46226 g [22] Filed: Apr. 28, 1972 Primary Examiner-Eli Lieberman [2]] App! No 248 706 Attorney-R. S. Sciascia et al.

' 57 B T A T [52] 11.8. C1 343/837, 343/840, 343/872 1 A S R 511 1111, C1. ..H01q 19/10 A radlatmg cone antenna havms a com! reflectms 581 Field of Search 343/837, 838, 840, Surface and a Parabolic reflecting Surface in spacial 343/914, 872; 240/4l.1, 41.35 C, 41.37, lationship and surrounding said conical reflecting sur- 4135 R, 4135, 4425 face. A linear directive radiator is positioned at the focus of the parabolic reflecting surface and energy {56] References Cited from the radiator is reflected from the parabolic re- UNITED STATES PATENTS flecting surface to the conical reflecting surface which, in turn, reflects the energy in a constant phase front. 1,738,304 12/1929 Laurent 240/4135 C 1,857,120 5/1932 Transom .Q 240/4137 5 Claims, 5 Drawing Figures RADIATING CONE ANTENNA STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used'by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates to a radio frequency antenna and more particularly to an antenna having first and second reflecting surfaces for transmitting energy in a, constant phase front.

Antennas having parabolic reflectors are widely used for directing beams of radio frequency energy. Generally, a beam'of energy from a radiator is projected at a small angle tothe axis of a parabolic reflector and the radiator is located on the axis at substantially the focal point of the reflector. The radiating system including the parabolic reflector is arrangedto be oriented both in elevation and in azimuth by suitable mechanical means so that the axis of'the paraboloid can be directed at a target. One such antenna system is shown and described in U.S. Pat. No. 2,541,806, entitled, Beam Antenna System, which issued Feb. I3, 1951-, to Burton P. Brown, Jr. Inthis patented .device, the antenna member is a dipole'whichislocatedat or near the focus of a paraboloid reflector andthe axis of the reflector passes through the dipole at or near the mid-- point thereof. A source of signal energy isprovidedfor exciting the dipole and this source produces pulses of oscillations of high frequency energy. Means is pro vided for shiftingthe antennabe'am pattern from'coincidenee with the axis of the reflector andfor rotating the antenna assembly so that arotating beam willbe projected.

SUMMARY OF THE INVENTION The present invention relates to a radio frequency antenna for reflecting energy along a constant phase front. A conical reflecting surfaceis provided and a parabolic reflecting surface is spacedfrom and surrounds the conicalreflecting surface. A feed mechanism is positioned at the focus of the parabolic reflector and energy from the feed mechanismis reflected from 4 the parabolic reflector to the conical-reflector. The conical reflector, in turn, reflects energyalong a line of constant phase, which is the basic criteria for maximum antenna gain.

BRIEF DESCRIPTIONOF THE DRAWINGS DESCRIPTION OF THE PREFERRED 1 EMBODIMENT Referring first to FlGql of the drawing which illustrates a prior art configuration of a parabolic reflector, the point of feed, A, is located at the focus of the parabolic curve 11 and waves which are reflected from the parabola parallel with the focal axis arrive at line C with equal phase. The path lengths of AB,C,, AB C AB C and AB C are equal. The use of parabolic reflectors in the antenna art is more fully described on pages 336-350 of the text, Antennas, by John D. Kraus, McGraw-Hill Book Company, Inc. 1950).

Referring now to FIG. 2 of the drawing, the present invention utilizes a parabolic reflector wherein the reflector is positioned so that its focal axis is parallel to the line ,C, which represents a constant phase front. Electromagnetic energy emitted from point source A, which is located at the focus of the parabolic curve 1 l, is reflected from a reflector represented by curve 11 to a second reflector represented by straight line 12. In FIG. 2 of the drawing, the path lengths of AB,B,C,, AB B' C and'AB B' C are equal.

By rotation of curve 11 and line 12 about axis D, parabolic surface 13 is generated which has point A as a radiating feed point, as shown in FIGS. 3 and 4 of the drawing. Feed point A is located as the focus of surface 13. Surface 14, which is generated by the rotation of line 12, is a cone. By way of example, angle 0 might be 90, and surface 14 would be a right angle cone. It can be seen that the altitude of-the cone is perpendicular to the focal axis of parabolic surface 13.

Referring now to FIG. 5 of the drawing, there is shown a feed element 15 which isenergized from circular waveguide 16. Itis desirable to locate the feed point at the apex of the cone surface 14, with the apex also being the focus for parabolic surface 13. Feed element 15 might be any conventional rear feed primary anthe rays of electromagnetic energy which are more rearwardly directed are at greater field strength. For example, referring to FIG. 5 of the drawing, ray F would have a greater field strength than ray G. When ray F is reflected from conical surface 14, however, it will be further from feed 15 than ray G. Thus, rays refleeting fromsurface 14 will be at'a lower intensity as a the feed is approached. This permits larger feed structures to be used without having the usual severeshadowing which results in Iowergain and also pattern distortion is conventional parabolic reflector antennas. Also the impedance mismatch resulting from energy reflecting back into the feed is minimized, or elimi nated and, therefore, larger RF bandwidths can be achieved.

The conical shape of surface 14 provides a convenient mechanical support of large feed structure and either all or part of a transmitting and receiving RF system can be packaged in the inner cone space. The advantages to be gained from this arrangement are the elimination of RF rotary couplings, and shortening of transmit and receiver RF lines thereby resulting in minimum energy loss and improved noise figure. If desired, the outer surface of reflector 17 can be made spherical and positioned in a socket type of gimbal for direction purposes.

As shown in FIG. 5 of the drawings, theforward edge of reflector 17 can extend beyond the end of feed 1 spillover effect common to a conventional parabolic antenna is avoided thereby providing a very low noise" antenna having high efflciency. Additionally, a flat sheet of dielectric material 18 can be fitted to the front of reflector 17 to serve as a radome and to permit a simple means of pressurization, if desired.

The embodiment shown in FIGS. 3, 4, and 5 of the drawing can be elliptical in shape or of other configuration without departing from the scope of the invention. Also this invention could apply equally well to a visible spectrum and to other RF spectrums which use a parabolic reflector in receiving or transmitting energy. By way of example, the present invention could be used with a carbon-arc search light whereby energy would not be redirected back to the lamp thereby providing for cooler operation.

It can thus be seen that the present invention providesan improved parabolic reflector antenna which does not have many of the inherent disadvantages common to presently used reflector antennas.

I claim:

1. A parabolic reflector antenna comprising:

a conical reflector,

an annular parabolic reflector surrounding said conical reflector with the focal axis of said parabolic reflector being perpendicular to the altitude of said conical reflector, and an antenna feed positioned at the focus of said parabolic reflector whereby energy radiating from said antenna feed is reflected from said parabolic reflector to said conical reflector which reflects energy along a line of constant phase. 2. A parabolic reflector antenna as set forth in claim 1 wherein the configuration of said conical reflector is a right angle cone.

3. A parabolic reflector antenna as set forth in claim 1 wherein the apex of said conical reflector is located on the focal axis of said parabolic reflector.

4. A parabolic reflector antenna as set forth in claim 1 wherein the forward edge of said parabolic antenna extends beyond said antenna feed.

5. A parabolic reflector antenna as set forth in claim 4 wherein the forward edge of said parabolic antenna is covered with a flat radome. 

1. A parabolic reflector antenna comprising: a conical reflector, an annular parabolic reflector surrounding said conical reflector with the focal axis of said parabolic reflector being perpendicular to the altitude of said conical reflector, and an antenna feed positioned at the focus of said parabolic reflector whereby energy radiating from said antenna feed is reflected from said parabolic reflector to said conical reflector which reflects energy along a line of constant phase.
 2. A parabolic reflector antenna as set forth in claim 1 wherein the configuration of said conical reflector is a right angle cone.
 3. A parabolic reflector antenna as set forth in claim 1 wherein the apex of said conical reflector is located on the focal axis of said parabolic reflector.
 4. A parabolic reflector antenna as set forth in claim 1 wherein the forward edge of said parabolic antenna extends beyond said antenna feed.
 5. A parabolic reflector antenna as set forth in claim 4 wherein the forward edge of said parabolic antenna is covered with a flat radome. 